<template>
<ul class="list">
    <li class="item"
        v-for="item of letters"
        :key="item"
        :ref="item"
        @touchstart="hangleTouchStart"
        @touchmove="hangleTouchMove"
        @touchend="hangleTouchEnd"
        @click="handletterClick"
    >{{item}}</li>
</ul>
</template>
<script>
export default{
  name: 'CityAlphabet',
  props: {
    cities: Object
  },
  computed: {
    letters () {
      const letters = []
      for (let i in this.cities) {
        letters.push(i)
      }
      return letters
    }
  },
  data () {
    return {
      touchStatus: false,
      startY: 0,
      timer: null
    }
  },
  updated () {
    this.startY = this.$refs['A'][0].offsetTop
  },
  methods: {
    handletterClick (e) {
      this.$emit('change', e.target.innerText)
    },
    hangleTouchStart () {
      this.touchStatus = true
    },
    hangleTouchMove (e) {
      if (this.touchStatus) {
        if (this.timer) {
          clearTimeout(this.timer)
        }
        this.timer = setTimeout(() => {
          const touchY = e.touches[0].clientY - 79
          const index = Math.floor((touchY - this.startY) / 20)
          if (index >= 0 && index < this.letters.length) {
            this.$emit('change', this.letters[index])
          }
        }, 16)
      }
    },
    hangleTouchEnd () {
      this.touchStatus = false
    }

  }
}
</script>
<style lang="stylus" scoped>
 @import '~styles/varibles.styl';
  .list
    display: flex
    flex-direction: column
    justify-content: center
    position: absolute
    top: 1.58rem
    right: 0
    bottom: 0
    width: .4rem
    .item
     line-height: .4rem
     text-align: center
     color: $bgColor
</style>
